1. Field of the Invention
The present invention relates to an image forming system that binds a stack of sheets by wrapping it with a cover page in the shape of a horizontal U.
2. Description of the Related Art
Binding apparatuses are known (see Patent Document 1) that carry out simple binding of a stack of a plurality of sheets on which images have been formed by a copying machine, or a printer, etc., by wrapping the stack of sheets with a cover page bent in the shape a horizontal U. An outline of a general binding technology is as follows. Firstly, a stack of sheets is prepared by accumulating and aligning a plurality of sheets on which images have been formed. Next, an adhesive such as gum, etc., is coated on one surface of the accumulated and aligned stack of sheets. Further, the cover sheet is conveyed and made to stop at a prescribed position, and the cover sheet is adhered to the surface of the stack of sheets on which the adhesive has been coated. Using this procedure, the stack of sheets and the cover sheet become bonded thereby forming a book.
An example of a book formed by a binding apparatus is shown in FIG. 1. FIG. 1(a) shows the state in which the cover sheet S2 has not been folded, and FIG. 1(b) shows the state in which the cover sheet S2 has been folded. S3 is constituted by the plurality of sheets S1 and the cover sheet S2, and is the form in which the cover sheet S2 wraps the stack of sheets S1 in the form of a horizontal U. In the following, S3 is called a wrapped book. In the final form of the wrapped book S3, the side edge part S1E of the sheets S1 and the side edge part S2E of the cover sheet S2 are aligned. The cove sheet S2 has, as is shown in FIG. 1(a), a front cover area a, a spine cover area b, and a back cover area c.
FIG. 2 shows a development drawing of the cover sheet S2. As is shown in FIG. 2, the front cover image G1 has been formed in the front cover area a, and a back cover image G2 has been formed in the back cover area c, and the front cover image G1 and the back cover image G2 are separated at a spacing X. The spine cover area b is present in between the front cover area a and the back cover area c, and the width of the spine cover area b (hereinafter referred to as the spine cover width) varies depending on the number of sheets S1 in the book. In other words, it is necessary to determine exactly the spine cover width in order to form the front cover image G1 and the back cover image G2 at accurate positions on the cover sheet S2.
As a method of determining the spine cover width, there is the method disclosed in Patent Document 2. In the technology described in Patent Document 2, the size of the spine cover part of the cover sheet is calculated using the data related to the thickness of one sheet, the data related to the toner thickness based on the amount of toner used per sheet, and the number of sheets.
Patent Document 1: Japanese Unexamined Patent Application Open to Public Inspection No. 2005-335262
Patent Document 2: Japanese Unexamined Patent Application Open to Public Inspection No. Hei 10-167557
However, since the spine cover width is affected by the variations in the thickness of one sheet of paper, the amount of curling of the sheet, etc., in the method of calculating it based on the data described in Patent Document 2 and the number sheets, it is not possible to determine exactly the spine cover width, and it is not possible to form the cover sheet image, etc., at an accurate position in the cover sheet.